chore: modular monolith folder split (no behavior change)

app/api/roster.py

@@ -0,0 +1,13 @@
+"""
+API Aggregation Layer - Roster endpoints
+Aggregates roster data from all feature modules
+"""
+from fastapi import APIRouter
+
+router = APIRouter(prefix="/api/roster-aggregation", tags=["roster-aggregation"])
+
+# TODO: Implement unified roster endpoints that combine data from
+# app.seismo and app.slm modules
+
+# For now, individual feature modules expose their own roster APIs
+# Future: Add cross-feature roster aggregation here